21. It was during this time that Jenner revisited the connection between cowpox and smallpox. 22. Jenner was the first to prove the effectiveness of vaccination with cowpox using experimentation. 23. He noted that inoculation with live cowpox afforded protection against the more dangerous smallpox. 24. The cowpox virus can infect humans, though the resulting disease is usually relatively mild. 25. At some point, the virus in use was no longer cowpox , but vaccinia. 26. Dr . Adams believed ( erroneously ) that cowpox and smallpox were the same disease. 27. Four orthopoxviruses cause infection in humans : variola, vaccinia, cowpox , and monkeypox. 28. On questioning, this subject had never had smallpox, but had previously contracted cowpox . 29. The outbreaks were traced to imported cowpox vaccine contaminated with foot-and-mouth virus. 30. Vaccinia, cowpox , and monkeypox viruses can infect both humans and other animals in nature.
